An evaluation of the usefulness of single pass albumin dialysis: key role of dialysate flow rate

In their article in Critical Care, Sponholz et al. [1] compared two devices: the molecular adsorbent recirculating system (MARS) and single pass albumin dialysis (SPAD). As Sponholz et al. claim, SPAD is not an effective method for achieving a significant decrease in the concentration of bile acids, creatinine or urea, because a single SPAD procedure induces a 7.62 % (median) reduction in the level of bile acids and an increase in the concentrations of creatinine and urea by respectively 5.04 % (median) and 4.69 % (median), compared with pre-dialysis levels [1]. In contrast, our as yet unpublished study demonstrates that SPAD can effectively reduce not only the level of bile acids but also the concentration of ammonia. Based on our study, the application of the SPAD method with a dialysate flow rate of 1000 ml/h for a total of around 10 h reduces the level of bile acids by 21.9 % (median) and ammonia by 16.25 % (median). A question arises as to the possible causes of such discrepancies. Since continuous venovenous haemodialysis was performed in both studies, the divergence cannot be attributed to the technique. In our view, this divergence is associated with several factors. One of these factors is the difference in dialysate flow rate. An albumin dialysate flow rate of 700 ml/h is highly insufficient. Taking into consideration the results obtained by Sponholz et al., an increase in the albumin dialysate flow rate to at least 1000 ml/h appears to be a necessary precondition to ensure effective elimination of bile acids. Also, the methodology adopted for the study is questionable. In our opinion, comparing the effectiveness of urea and creatinine elimination at radically different dialysate flow rates (SPAD 700 ml/h vs MARS 2000 ml/h) is unjustified and may lead to erroneous conclusions, which in fact occurred [1]. Differences in efficacy between the MARS and SPAD procedures reported in the article in question may also be related to inappropriately selected haemofilters in the extracorporeal blood purification systems under comparison. Furthermore, Sponholz et al. [1] pointed out metabolic derangements and electrolyte disturbances, particularly in SPAD using regional citrate anticoagulation. In our view, increasing the dialysate flow rate would significantly contribute to preventing the irregularities noted in the study. On the other hand, we believe that the risk of citrate overdose during liver dialysis, but also during continuous venovenous haemodialysis, is very low [2–4].